1. Field of the Invention
The present invention relates to a material estimation apparatus, a material estimation program and a method of estimating materials which estimates physical properties of objects while taking a contact resistance into consideration.
2. Related Background Art
A device simulation is inevitable for effective design of LSIs. It is necessary for the device simulation to incorporate various phenomenons in a semiconductor device as a part of an estimation system. There is a contact resistance as one of the phenomenons.
FIG. 1 shows a typical cross sectional view of an insulated gate transistor (hereinafter, called as a MISFET). There is a contact portion between a metal and a semiconductor in most of the semiconductor devices. In the case of FIG. 1, a surface between a source silicide and a source diffusion layer, and a surface between a drain silicide and a drain diffusion layer correspond to contact portions. The contact resistance occurs in these contact portions. The contact resistance causes current drop and heat generation.
In the conventional technique, the simplest method taking the contact resistance into consideration is to provide an external resistor connected to a terminal electrode as shown in FIG. 21. In this method, it is impossible to take into consideration influences of potential drop due to the contact resistance in the device and heat generation.
As a method of performing simulation by importing the influence of the contact resistance in the device, there is a method as shown in FIG. 22. That is, the value of the contact resistance ρc indicated by user or automatically calculated is converted into the electric resistivity ρs. That is, a grid interval Δx is provided between the metal and the semiconductor. The electric resistivity ρs obtained by dividing the value ρc of the contact resistance by the grid interval is set to the grid interval.
According to this method, even if the grid interval Δx changes, the amount of the current is hardly affected as shown in FIG. 23. The reason is because the electric resistivity ρs is set in accordance with the grid interval Δx so that the potential difference at the contact portion hardly changes, even if the grid interval Δx changes, as shown in FIG. 24. In FIG. 24, the voltage difference is Δφ1 in the case of the grid interval Δx=5 nm, and the voltage difference is Δφ2 in the case of the grid interval Δx=50 nm. As shown in FIG. 24, even if the grid interval changes, it turns out that the voltage difference is almost equal.
Thus, even in the conventional technique, without being affected on the grid interval, it is possible to perform the simulation which allows the value of the contact resistance to reflect to the amount of the current.
However, according to the method of FIG. 22, there is a problem in which the amount of the heat generation due to the contact resistance depends on the grid interval.
FIG. 25 shows grid temperature distribution in the substrate surface portion of a MISFET. Grid temperature in a contact portion between the silicide and the diffusion layer changes in accordance with the grid interval. The reason is because the value of electrical field is different from each of the grid intervals affected by the contact resistance.
More specifically, in FIG. 25, when the grid interval affected by the contact resistance is Δx, and the voltage difference is Δφ, Δφ does not largely change depending on Δx. However, consumption power in the contact portion between the silicide and the diffusion layer is calculated by the current density J and the electric field E, and the electric field E is given by (−Δφ/Δx). Because of this, even if Δφ is constant, if Δx is different, the consumption power is different from each other. As a result, the difference of the grid temperature distribution appears, as shown in FIG. 25.
Thus, conventionally, even if the simulation is performed while taking the contact resistance into consideration, the results of the simulation relating to the grid temperature differs in accordance with the grid interval, and the prediction result of tolerance such as breakdown due to heat generation of the contact resistance portion also changes in accordance with the grid interval.